spoj 104 Highways(生成树计数)

http://www.spoj.pl/problems/HIGH/

　　题目写着答案不超过long long，应该是中间过程爆long long了，所以用整型做的时候在辗转相除的过程超时了，后来改成double就过了！

代码如下：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

//typedef long long ll;
typedef double ll;
const double eps = 1e-8;
const int maxSize = 15;
int curSize = maxSize;

struct Mat {
    ll val[maxSize][maxSize];

    Mat() {
        for (int i = 0; i < curSize; i++) {
            for (int j = 0; j < curSize; j++) {
                val[i][j] = 0;
            }
        }
    }
    ll Det() {
        ll ret = 1;

        for (int p = 1; p < curSize; p++) {
            for (int l = p + 1; l < curSize; l++) {
//                while (val[l][p]) {
                while (fabs(val[l][p]) > eps) {
//                    int k = val[p][p] / val[l][p];
                    double k = val[p][p] / val[l][p];

                    for (int i = p; i < curSize; i++) {
                        val[p][i] -= val[l][i] * k;
                        swap(val[p][i], val[l][i]);
                    }
                    ret = -ret;
                }
            }
//            if (!val[p][p]) return 0;
        }

        for (int i = 1; i < curSize; i++) {
            ret *= val[i][i];
        }

        return ret;
    }
} mat;

void makeMat(int m) {
    int s, t;

    mat = Mat();
    while (m--) {
        scanf("%d%d", &s, &t);
        s--; t--;
//        if (!mat.val[s][t]) {
        if (fabs(mat.val[s][t]) < eps) {
            mat.val[s][t] = mat.val[t][s] = -1;
            mat.val[s][s]++; mat.val[t][t]++;
        }
    }
}

int main() {
    int T, m;

//    freopen("in", "r", stdin);
    scanf("%d", &T);
    while (T-- && ~scanf("%d%d", &curSize, &m)) {
        makeMat(m);
//        printf("%lld\n", mat.Det());
        printf("%.0f\n", mat.Det());
    }

    return 0;
}

——written by Lyon